The invention relates to a coating apparatus with a sputtering cathode bearing a set of magnets and disposed within a coating chamber, which has an electrode insulated electrically from the coating chamber and connected to negative potential, and in which the target forming the material to be sputtered is fastened on the side of the electrode facing away from the magnet set, while on the side of the electrode facing away from the target a pressure equalizing chamber is provided which has a vacuum connection for establishing a vacuum counteracting the vacuum in the coating chamber.
A coating apparatus of this kind is the subject of WO 90/13137. In sputtering cathodes used in such coating apparatus and known as "magnetron cathodes," it is desirable for a very strong magnetic field to act on the target surface. Therefore, the distance between the magnet set and the target should be as small as possible, and this requires that the electrode wall to be as thin as possible. In order to avoid the danger that the cathode together with the target might bend in the case of great pressure differences and great target surface areas, the known cathode has on its side facing away from the target a pressure equalizing chamber in which the same vacuum prevails as in the coating chamber.
Unsolved in the known coating apparatus is the problem of the formation of undesired secondary plasmas at the back of the sputtering cathode. Also, the known coating apparatus is relatively small, and in it the coating chamber has the same cross section as the pressure equalizing chamber.